The present invention relates to a system for the direct sequencing of polymers such as DNA and RNA and proteins by passing the polymer through a nanoscale pore and measuring an electrical signal modulated by the polymer passing through the pore.
Genetic information may be encoded in a molecule of deoxyribonucleic acid (DNA) as a sequence of nucleotides: (guanine, adenine, thymine, and cytosine). Discovering the sequence of these nucleotides in DNA and other similar molecules is a foundational technology in biological studies.
One promising method of sequencing is “nanopore sequencing” in which a single strand of DNA, forming half of the DNA helix, is passed through a nanoscale opening in a membrane between two reservoirs. This nanopore opening may, for example be a biological pore, a solid state pore, a semiconductor pore (nano-channel) or a DNA synthesized channel held in a lipid bilayer. By a drying force, e.g. an electrical potential applied across the reservoirs, an ion flow is produced between the reservoirs pulling the strand of DNA through the nanopore. As the strand passes through the nanopore, it modulates the ion current through the nanopore as a function of the size of the nucleotide, which partially obstructs the nanopore. This fluctuation in the ion current may then be analyzed to determine the nucleotide sequence. An example system of nanopore sequencing is described in PCT patent publication WO2008102120 entitled: Lipid Bilayer Sensor System, hereby incorporated by reference.
The electrical signals produced by changes in ion current through a nanopore with different nucleotides are very small in amplitude and most importantly short in time span. For this reason, it can be hard to obtain reliable measurements having sufficient resolution to distinguish between different molecules in the sequence.
U.S. patent application Ser. No. 13/786,880, assigned to the assignee of the present application and hereby incorporated by reference, describes a method of analyzing the operation of nanopore ion channels using changes in impedance of a nanopore device measured at radio frequencies.